Appointments + booking conflict/overlapping bookings

I have discovered a pretty significant problem on my appointments + 1.4 plugin and my site. I am using the Durations Addon for this plugin. Our main issue at the moment is that when a room is booked from say 11am to 1pm (2 hours) the room is blocked off on the system for the two hours which is great. However when the meeting commences at 11am the room immediately becomes available at 11.01am on the system and another client/user can book the room, even though it is in use of course!!

We had an issue this morning where two clients overlapped times because of this issue and to say the least it was very embarrassing for us. Hopefully you can guide me to a fix asap where the room is not available on the system until the meeting ends and not when the meeting begins! I have attached some of my settings here in a screenshot incase it helps. I am desperate for a fix as I have discovered a number of overlaps. Thanks in advance here.